784 research outputs found
Cosmic String Cusps with Small-Scale Structure: Their Forms and Gravitational Waveforms
We present a method for the introduction of small-scale structure into
strings constructed from products of rotation matrices. We use this method to
illustrate a range of possibilities for the shape of cusps that depends on the
properties of the small-scale structure. We further argue that the presence of
structure at cusps under most circumstances leads to the formation of loops at
the size of the smallest scales. On the other hand we show that the
gravitational waveform of a cusp remains generally unchanged; the primary
effect of small-scale structure is to smooth out the sharp waveform emitted in
the direction of cusp motion.Comment: RevTeX, 8 pages. Replaced with version accepted for publication by
PR
The stochastic background: scaling laws and time to detection for pulsar timing arrays
We derive scaling laws for the signal-to-noise ratio of the optimal cross-correlation statistic, and show that the large power-law increase of the signal-to-noise ratio as a function of the observation time T that is usually assumed holds only at early times. After enough time has elapsed, pulsar timing arrays enter a new regime where the signal to noise only scales as . In addition, in this regime the quality of the pulsar timing data and the cadence become relatively unimportant. This occurs because the lowest frequencies of the pulsar timing residuals become gravitational-wave dominated. Pulsar timing arrays enter this regime more quickly than one might naively suspect. For T = 10 yr observations and typical stochastic background amplitudes, pulsars with residual root-mean-squares of less than about 1 μs are already in that regime. The best strategy to increase the detectability of the background in this regime is to increase the number of pulsars in the array. We also perform realistic simulations of the NANOGrav pulsar timing array, which through an aggressive pulsar survey campaign adds new millisecond pulsars regularly to its array, and show that a detection is possible within a decade, and could occur as early as 2016
On the size of the smallest scales in cosmic string networks
We present a method for the calculation of the gravitational back reaction
cutoff on the smallest scales of cosmic string networks taking into account
that not all modes on strings interact with all other modes. This results in a
small scale structure cutoff that is sensitive to the initial spectrum of
perturbations present on strings. From a simple model, we compute the cutoffs
in radiation- and matter-dominated universes.Comment: 4 pages, revte
GravEn: Software for the simulation of gravitational wave detector network response
Physically motivated gravitational wave signals are needed in order to study
the behaviour and efficacy of different data analysis methods seeking their
detection. GravEn, short for Gravitational-wave Engine, is a MATLAB software
package that simulates the sampled response of a gravitational wave detector to
incident gravitational waves. Incident waves can be specified in a data file or
chosen from among a group of pre-programmed types commonly used for
establishing the detection efficiency of analysis methods used for LIGO data
analysis. Every aspect of a desired signal can be specified, such as start time
of the simulation (including inter-sample start times), wave amplitude, source
orientation to line of sight, location of the source in the sky, etc. Supported
interferometric detectors include LIGO, GEO, Virgo and TAMA.Comment: 10 Pages, 3 Figures, Presented at the 10th Gravitational Wave Data
Analysis Workshop (GWDAW-10), 14-17 December 2005 at the University of Texas,
Brownsvill
Gravitational-Wave Stochastic Background from Kinks and Cusps on Cosmic Strings
We compute the contribution of kinks on cosmic string loops to stochastic
background of gravitational waves (SBGW).We find that kinks contribute at the
same order as cusps to the SBGW.We discuss the accessibility of the total
background due to kinks as well as cusps to current and planned gravitational
wave detectors, as well as to the big bang nucleosynthesis (BBN), the cosmic
microwave background (CMB), and pulsar timing constraints. As in the case of
cusps, we find that current data from interferometric gravitational wave
detectors, such as LIGO, are sensitive to areas of parameter space of cosmic
string models complementary to those accessible to pulsar, BBN, and CMB bounds.Comment: 24 pages, 3 figure
Chi-square test on candidate events from CW signal coherent searches
In a blind search for continuous gravitational wave signals scanning a wide
frequency band one looks for candidate events with significantly large values
of the detection statistic. Unfortunately, a noise line in the data may also
produce a moderately large detection statistic.
In this paper, we describe how we can distinguish between noise line events
and actual continuous wave (CW) signals, based on the shape of the detection
statistic as a function of the signal's frequency. We will analyze the case of
a particular detection statistic, the F statistic, proposed by Jaranowski,
Krolak, and Schutz.
We will show that for a broad-band 10 hour search, with a false dismissal
rate smaller than 1e-6, our method rejects about 70 % of the large candidate
events found in a typical data set from the second science run of the Hanford
LIGO interferometer.Comment: proceedings of GWDAW8, 2003 conference, 12pages, 6 figure
Reconstructing the calibrated strain signal in the Advanced LIGO detectors
Advanced LIGO's raw detector output needs to be calibrated to compute
dimensionless strain h(t). Calibrated strain data is produced in the time
domain using both a low-latency, online procedure and a high-latency, offline
procedure. The low-latency h(t) data stream is produced in two stages, the
first of which is performed on the same computers that operate the detector's
feedback control system. This stage, referred to as the front-end calibration,
uses infinite impulse response (IIR) filtering and performs all operations at a
16384 Hz digital sampling rate. Due to several limitations, this procedure
currently introduces certain systematic errors in the calibrated strain data,
motivating the second stage of the low-latency procedure, known as the
low-latency gstlal calibration pipeline. The gstlal calibration pipeline uses
finite impulse response (FIR) filtering to apply corrections to the output of
the front-end calibration. It applies time-dependent correction factors to the
sensing and actuation components of the calibrated strain to reduce systematic
errors. The gstlal calibration pipeline is also used in high latency to
recalibrate the data, which is necessary due mainly to online dropouts in the
calibrated data and identified improvements to the calibration models or
filters.Comment: 20 pages including appendices and bibliography. 11 Figures. 3 Table
Accurate calibration of test mass displacement in the LIGO interferometers
We describe three fundamentally different methods we have applied to
calibrate the test mass displacement actuators to search for systematic errors
in the calibration of the LIGO gravitational-wave detectors. The actuation
frequencies tested range from 90 Hz to 1 kHz and the actuation amplitudes range
from 1e-6 m to 1e-18 m. For each of the four test mass actuators measured, the
weighted mean coefficient over all frequencies for each technique deviates from
the average actuation coefficient for all three techniques by less than 4%.
This result indicates that systematic errors in the calibration of the
responses of the LIGO detectors to differential length variations are within
the stated uncertainties.Comment: 10 pages, 6 figures, submitted on 31 October 2009 to Classical and
Quantum Gravity for the proceedings of 8th Edoardo Amaldi Conference on
Gravitational Wave
Discovery and Follow-up of Rotating Radio Transients with the Green Bank and LOFAR Telescopes
We have discovered 21 Rotating Radio Transients (RRATs) in data from the
Green Bank Telescope (GBT) 350-MHz Drift-scan and the Green Bank North
Celestial Cap pulsar surveys using a new candidate sifting algorithm. RRATs are
pulsars with sporadic emission that are detected through their bright single
pulses rather than Fourier domain searches. We have developed {\tt RRATtrap}, a
single-pulse sifting algorithm that can be integrated into pulsar survey data
analysis pipelines in order to find RRATs and Fast Radio Bursts. We have
conducted follow-up observations of our newly discovered sources at several
radio frequencies using the GBT and Low Frequency Array (LOFAR), yielding
improved positions and measurements of their periods, dispersion measures, and
burst rates, as well as phase-coherent timing solutions for four of them. The
new RRATs have dispersion measures (DMs) ranging from 15 to 97 pc cm,
periods of 240 ms to 3.4 s, and estimated burst rates of 20 to 400 pulses
hr at 350 MHz. We use this new sample of RRATs to perform statistical
comparisons between RRATs and canonical pulsars in order to shed light on the
relationship between the two populations. We find that the DM and spatial
distributions of the RRATs agree with those of the pulsars found in the same
survey. We find evidence that slower pulsars (i.e. ms) are
preferentially more likely to emit bright single pulses than are faster pulsars
( ms), although this conclusion is tentative. Our results are consistent
with the proposed link between RRATs, transient pulsars, and canonical pulsars
as sources in various parts of the pulse activity spectrum.Comment: 18 pages, 13 figures, 5 tables, published in Ap
Optimal strategies for continuous gravitational wave detection in pulsar timing arrays
Supermassive black hole binaries (SMBHBs) are expected to emit continuous
gravitational waves in the pulsar timing array (PTA) frequency band
(-- Hz). The development of data analysis techniques aimed at
efficient detection and characterization of these signals is critical to the
gravitational wave detection effort. In this paper we leverage methods
developed for LIGO continuous wave gravitational searches, and explore the use
of the -statistic for such searches in pulsar timing data. Babak &
Sesana 2012 have already used this approach in the context of PTAs to show that
one can resolve multiple SMBHB sources in the sky. Our work improves on several
aspects of prior continuous wave search methods developed for PTA data
analysis. The algorithm is implemented fully in the time domain, which
naturally deals with the irregular sampling typical of PTA data and avoids
spectral leakage problems associated with frequency domain methods. We take
into account the fitting of the timing model, and have generalized our approach
to deal with both correlated and uncorrelated colored noise sources. We also
develop an incoherent detection statistic that maximizes over all pulsar
dependent contributions to the likelihood. To test the effectiveness and
sensitivity of our detection statistics, we perform a number of monte-carlo
simulations. We produce sensitivity curves for PTAs of various configurations,
and outline an implementation of a fully functional data analysis pipeline.
Finally, we present a derivation of the likelihood maximized over the
gravitational wave phases at the pulsar locations, which results in a vast
reduction of the search parameter space.Comment: 11 pages, 5 figure
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